The objective of the proposed research is to investigate the ionic and metabolic events underlying the receptor potential of visual cells. The long-term goal of this research is to arrive at a more complete understanding of the transduction of visual information into neural events at the receptor level under normal and abnormal conditions. Research will be done on hyperpolarizing photoreceptors of invertebrate (molluscan) and vertebrate (amphibian) eyes. Individual eyes will be isolated and mounted in a perfusion chamber so that intracellular recordings of membrane potential can be obtained during light and dark conditions in different ionic media, in the presence of metabolic inhibitors, at different temperatures and under various oxygenation levels. The investigation will be concerned with showing which ions are involved in maintaining the membrane potential of photoreceptors in light and dark conditions and which permeabilities change in response to different levels of illumination. The experiments will be used to examine the role cellular metabolism plays in maintaining membrane permeability and in determining which permeabilities change when specific metabolic pathways are inhibited. A second aspect of this research will be to provide quantitative information about the anatomy of hyperpolarizing receptor cells. Data about the shape of the soma and the presumed photoreceptive region of the cell, their volume and surface area will be obtained so that a geometrical model of the cell can be constructed. Electrical measurements of the receptor's passive membrane properties (total resistance, time constant and the shape of the voltage transient to a step of current) will be made with intracellular recording and stimulating techniques to determine which of the possible geometrical models best express fit the anatomical data. With this information it should eventually be possible to express electrical and ionic data in terms of specific cell surface area and volume measurements.